Over the last few days there have been several reports that suggest SARS-CoV-2, the virus that causes the COVID-19 disease, is not mutating significantly. By analyzing the genetic material of different samples of the virus, collected from varying locations throughout the outbreak, scientists are able to learn about how it spreads. News that the virus is slow to mutate is positive in terms of vaccine development, as it indicates that when one is created it could be effective for many years.
Viruses are expected to evolve over time, as they imperfectly replicate inside a host’s cells. Whilst some adverse mutations are removed by natural selection, others can thrive. However, in the case of SARS-CoV-2, scientists across the world have observed relatively little genetic mutation to the virus since the outbreak began.
Two teams of infectious disease researchers in Italy, a nation hit hard by the pandemic, have independently analyzed local samples of the coronavirus and compared their genomes to that of the virus when sequenced in China two months ago. Their preliminary results suggest the rapidly spreading virus’ genome is stable with few genetic variations.
"Our initial data show that this is a very stable RNA virus, with only five novel variants,” Professor Stefano Menzo, head of Virology at Ancona University Hospital, said in a statement. "Had we investigated other viruses we might have expected up to dozens of new mutations after so many infectious cycles in patients."
Menzo also explained how this could impact a potential vaccine. “A virus with a stable genome is good news for vaccine development because it indicates that the effectiveness of vaccines could be more consistent, possibly over many years.”
Another group working in the US told the Washington Post that they too have found only about four to 10 genetic differences between the strains infecting people in the US and the original virus in Wuhan.
“That’s a relatively small number of mutations for having passed through a large number of people,” Peter Thielen, a molecular geneticist at the Johns Hopkins University Applied Physics Laboratory, told the Washington Post. “At this point, the mutation rate of the virus would suggest that the vaccine developed for SARS-CoV-2 would be a single vaccine, rather than a new vaccine every year like the flu vaccine.”
As viral genomes are dynamic, the genetic material of SARS-CoV-2 could still diversify. However, according to a commentary by Nathan Grubaugh, an epidemiologist at the Yale School of Public Health, this is a natural part of the virus lifecycle and “we shouldn’t worry when a virus mutates during disease outbreaks.” In fact as the virus diversifies, it may enable clearer lineages of the disease to be mapped.
However, caution should still be exercised to ensure findings are not “over interpreted,” as sample sizes are still small and we are still early in the outbreak, scientists have warned. In a similar vein, concerns have also been raised in the scientific community about a preliminary study published earlier this month, which suggests a second strain of coronavirus has evolved which elicits a more severe case of COVID-19.
“So far, we don’t have any evidence linking a specific virus [strain] to any disease severity score,” Thielen told the Washington Post. “Right now, disease severity is much more likely to be driven by other factors.”